1. Technical Field
This invention relates generally to a carrier tape that is used to transport components from a component manufacturer to a different manufacturer or to an assembler that assembles the components into new products. More specifically, this invention relates to flexible carrier tapes for storing electronic surface mount components and for supplying those components seriatim to a machine.
2. Description of the Related Art
In the field of electronic circuit assembly, it is common to use robotic placement equipment to move electronic components such as resistors, capacitors, or memory chips from a supply source to a circuit board for attachment in a specific location on the circuit board. After attachment to the circuit board, the circuit board may be further incorporated into an electronic device.
High speed automated robotic placement equipment is often used for electronic circuit assembly, where a typical robotic component placement machine can place between 1,000 and 30,000 components per hour on circuit boards. More specifically, the placement of components on circuit boards is often accomplished with vacuum pick-up devices that draw vacuum pressure through small orifices. The vacuum pressure is sufficient to attract components to the vacuum pick-up devices from a supply source and this pressure is maintained while moving the components to their desired locations on circuit boards. The vacuum pressure is then sufficiently reduced to allow the components to detach from the vacuum devices. This sequence of picking up a component and placing it on a circuit board is repeated for each circuit board or series of circuit boards that require components to be affixed to their surfaces. The automated robotic placement equipment is programmed to perform this sequence of movements at a high speed. To keep the robotic placement equipment operating at high speeds through multiple cycles, the vacuum devices must be capable of picking up the required components during each cycle. Because the vacuum device orifices are typically quite small, it is advantageous to minimize contaminants near the orifices during operation of the vacuum devices to prevent clogging of the orifices.
A common way to supply components to robotic placement equipment is by a carrier tape. With a carrier tape, a component manufacturer typically loads components into a series of pockets that are precisely spaced along the length of the carrier tape, covers the components with a cover tape, and winds the loaded carrier tape into a roll or onto a reel. The loaded carrier tape may then be used to transport the components from the component manufacturer to another manufacturer or to an assembler, where the roll of carrier tape may be mounted within an assembly process. The carrier tape is typically unwound from the roll and automatically advanced toward a robotic pick-up location. As the carrier tape advances, the robotic placement equipment removes the cover tape, after which it removes the components from each succeeding pocket of the carrier tape, such as with a vacuum pick-up device, to assemble the components into new products.
One type of carrier tape, known as a punched carrier tape, is illustrated in U.S. Pat. No. 4,702,788 (Okui) and 5,203,143 (Gutentag). The pockets of punched carrier tapes are typically formed by die punching a series of holes through a strip of material that is slit from a sheet of the material having a thickness corresponding to the depth of the pockets to be formed. An adhesive tape is often adhered to one side of the strip of material so that some portion of the adhesive tape is exposed to the inside of the pocket, thereby creating the bottom of the pocket. To use a punched carrier tape, a component is typically placed onto the adhesive surface in each pocket, over which a cover strip may be affixed. The carrier tape may then be wound into a roll and transported to another assembler or manufacturer.
The strips of material used for punched carrier tapes are often strips of paper that are slit from larger sheets of paper. The processes of slitting the paper sheets into strips and punching holes into the strips of paper often creates residual fine dust particulates in the pockets and on the face of the carrier tape. These particulates can contaminate components that are placed in the pockets, which may make the components unusable. The particulates may also obstruct the small vacuum orifices of some robotic placement equipment, thereby decreasing the performance of the vacuum devices such that they can no longer pick up components, or may otherwise interfere with the ability of the robotic placement equipment to recognize and grasp components in the pockets. The vacuum equipment must then be serviced, which can be both expensive and time consuming.
Paper carrier tapes also cause other concerns. Carrier tape paper typically uses a filler, such as clay, which is abrasive to die punch tools. This causes accelerated wear of the tools and poor quality hole punching. The fact that paper carrier tapes are typically made of multiple paper layers laminated to each other also causes problems. In the presence of moisture, the paper layers tend to expand and change dimensions, which can cause delamination of the paper layers. In addition, these multiple paper layers tend to delaminate from each other when wound about a reel, particularly when the paper is thick. Therefore, the thickness of paper strips are often limited to about 1 millimeter (0.04 inch), which limits the thickness of components that can be stored in the carrier tape. Finally, because paper carrier tapes tend to be fairly rigid, they have an inherent tendency to unwind from a core about which they are wound and return to a linear position, which is an effect known as "watchspringing." Watch-springing leads to difficulty in handling reels of paper carrier tape in both loading and unloading operations.
To address some of the concerns associated with paper carrier tapes, it is known to make the strips of material from nonwoven materials, such as a layer of nonwoven polymeric fibers adhered together at their crossover points. One example of such a carrier tape is illustrated in U.S. Pat. No. 5,150,787 (Bird et al.). Nonwoven polymeric carrier tapes are typically more flexible (i.e., less prone to the watch-springing effect) and less abrasive than paper carrier tapes. In addition, the dust particulates generated when slitting and punching paper tapes are not generated when producing nonwoven polymeric carrier tapes. However, residual stray fibers can extend into the pockets and from the face of the carrier tape. These fibers can obstruct the small vacuum orifices of some robotic placement equipment, or may otherwise interfere with the ability of the robotic placement equipment to recognize and grasp components. In addition, the process of blowing microfibers for nonwoven polymeric materials can be expensive and complex.
Another material suggested for the strips of material used in punched carrier tapes is a multi-layer laminated polymeric foam structure, as in U.S. Pat. No. 4,657,137 (Johnson). This carrier tape requires the use of at least two separate layers and is produced by providing a flexible thin plastic or foam layer to which a strong and stable base layer is laminated. The base layer is selected to provided the desired strength for the tape structure.
In view of the disadvantages of conventional carrier tapes, it is therefore desirable to provide a low cost carrier tape that can be produced easily and inexpensively and that does not leave dust or stray fibers when slit and punched.